This invention relates to silicon carbide bodies and their production. It is particularly concerned with silicon carbide bodies (hereinafter referred to as "reaction-bonded silicon carbide bodies") produced by the reaction sintering of green bodies, formed from a coherent mixture of silicon carbide and carbon, in the presence of molten silicon (hereinafter referred to as "siliconising"). The production of such bodies is described, for example, in U.S. Pat. No. 3,495,939. They consist essentially of a substantially continuous matrix of silicon carbide particles bonded together and a substantially continuous free silicon phase. Nitrogen is also present as a natural impurity in commercially available material.
Reaction-bonded silicon carbide has a number of uses in which its good oxidation resistance, its wear resistance and its mechanical properties at high temperature are of value. Variation in electrical conductivity and other physical properties, notably thermal conductivity, to meet specific requirements increases its use. Thus thermal shock resistance requires a high thermal conductivity and spark or electrochemical machining is facilitated by a high electrical conductivity while electric resistance heaters demand a minimum of change in resistivity with change in temperature.